System and method for hybrid energy conversion

ABSTRACT

A system and method for conditioning DC power received from hybrid DC power sources is disclosed. A power conversion circuit is coupled to a respective DC power source to selectively condition the output power generated thereby to a DC bus voltage. The power conversion circuit includes a switch arrangement and capacitors arranged to provide a charge balancing in the power conversion circuit. A controller in operable communication with the switch arrangement receives inputs on a DC bus voltage and at least one parameter related to operation of the DC power source, and determines an adjustable voltage to be output from the conversion circuit to the DC bus based on the received inputs. The controller then selectively controls operation of the switch arrangement in order to generate the determined adjustable voltage.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 14/262,144, filed Apr. 25, 2014, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to electronic powerconversion and, more particularly, to a system and method for performinga power conversion on the power output from hybrid DC energy sources,such as a photovoltaic (PV) module and a battery, that allows for theoutput of the two DC sources to connect to a common DC distributionsystem.

In industry, it is becoming increasingly common for varying types ofenergy or power sources to be employed in combination with one anotherfor purposes of power generation and/or distribution. One common exampleis the use of photovoltaic (PV) systems in combination with DCbatteries. PV systems include PV modules arranged in arrays thatgenerate direct current (DC) power, with the magnitude of DC currentbeing dependent on solar irradiation and the magnitude of DC voltagedependent on ambient and solar cell temperature. The use of DC batteriesin conjunction with PV systems is often desirable, as the DC batteriesprovide for energy storage that allows for a number of features thatenhance power system operation and enable higher penetration of solarpower, while providing a backup source of power during times when solarirradiation is low or absent (e.g., at night).

However, it is recognized that systems that incorporate both PV systemsand DC batteries face restrictions with respect to sharing of the DCpower—as such sharing of DC power on a common DC bus may not be possibledue to the mismatch of the operating voltage between the batteries andthe PV systems. That is, for PV systems and batteries—as well as withcombinations of other alternative power sources—the power sourceterminal characteristics such as voltage, current, power flow direction,etc., will often vary greatly. While the use of separate specializedvoltage converters with each power source may help address thediscrepancies in terminal characteristics between the power sources, theuse of such converters can add to the overall cost and complexity of thepower system and may affect its reliability.

Therefore, it would be desirable to provide a system and a method thatenables the use of a mix of different energy sources (i.e., a hybridenergy system) and that links those energy sources for use in a commonsystem. Such a system and method should provide standardized andflexible conversion or interface circuits to link those energy sources,so as to provide flexible, highly efficient, bi-directional power flowat a lower cost.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, a DC power distributionsystem includes a DC bus and a plurality of DC power sources connectedto the DC bus each configured to generate an output power fortransmission to the DC bus, wherein the plurality of DC power sourcesinclude at least two different types of DC power sources havingdiffering voltage terminal output characteristics. The DC powerdistribution system also includes a power conversion circuit coupled toeach of the plurality of DC power sources to selectively condition theoutput power generated by its respective DC power source to a DC busvoltage, with each power conversion circuit having a standardizedconstruction so as to be identical to each of the other power conversioncircuits. Each power conversion circuit further comprises a switcharrangement comprising a plurality of switches operable in an open stateand a closed state, a plurality of capacitors arranged to provide acharge balancing in the power conversion circuit, the plurality ofcapacitors including a DC link capacitor, and a controller in operablecommunication with the switch arrangement, the controller beingprogrammed to receive a first input comprising a DC bus voltage presenton the DC bus, receive a second input comprising at least one parameterrelated to operation of the DC power source to which the respectivepower conversion circuit is coupled, determine an adjustable voltage tobe output from the conversion circuit to the DC bus based on thereceived first and second inputs, and selectively control operation ofeach of the plurality of switches in the switch arrangement in order togenerate the determined adjustable voltage.

In accordance with another aspect of the invention, a method ofconditioning an output power of hybrid DC power sources in a powerdistribution system includes generating a first output power from afirst DC power source and generating a second output power from a secondDC power source, the second DC power source being a different powersource than the first DC power source such that the second output powerhas a different voltage characteristic than the first output power. Themethod also includes performing a voltage conversion of the first outputpower by way of a first conversion circuit so as to generate a firstmodified voltage and performing a voltage conversion of the secondoutput power by way of a second conversion circuit so as to generate asecond modified voltage, the second conversion circuit having anidentical construction as the first conversion circuit. The methodfurther includes providing the first and second modified voltages to acommon DC bus to which the first and second DC power sources and firstand second conversion circuits are electrically coupled, whereinperforming the voltage conversion of the first and second output powersby way of the first and second conversion circuits each furthercomprises receiving a first input comprising a DC bus voltage present onthe DC bus, receiving a second input comprising at least one parameterrelated to operation of the DC power source to which the respectivepower conversion circuit is coupled, determining a modified voltage tobe output from the conversion circuit to the DC bus based on thereceived first and second inputs, and controlling operation of therespective conversion circuit in order to generate the determinedmodified voltage.

In accordance with yet another aspect of the invention, a DC powerdistribution system includes a DC bus and a plurality of DC powersources connected to the DC bus and configured to generate an outputpower for transmission to the DC bus, wherein the plurality of DC powersources include at least two different types of DC power sources havingdiffering voltage terminal output characteristics. The DC powerdistribution system also includes a voltage conversion circuitoperatively coupled to each of the plurality of DC power sources toselectively condition the DC power generated by its respective DC powersource or condition a DC power provided to its respective DC powersource to provide recharging thereto. Each of the voltage conversioncircuits has an identical construction and further includes a switcharrangement comprising a plurality of switches operable in an open stateand a closed state, a plurality of capacitors arranged to provide acharge balancing in the power conversion circuit, the plurality ofcapacitors including a DC link capacitor, and a controller in operablecommunication with the switch arrangement. The controller is programmedto receive a first input comprising a DC bus voltage present on the DCbus, receive a second input comprising at least one parameter related tooperation of the DC power source to which the respective powerconversion circuit is coupled, and determine an adjustable voltage to beoutput from the conversion circuit to the DC bus or to the DC powersource based on the received first and second inputs, the adjustablevoltage comprising a positive or negative voltage of desired magnitude.The controller is further programmed to selectively control operation ofeach of the plurality of switches in the switch arrangement in order togenerate the determined adjustable voltage.

These and other advantages and features will be more readily understoodfrom the following detailed description of preferred embodiments of theinvention that is provided in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a schematic diagram of a DC power distribution systemincluding voltage conversion circuits, according to an embodiment of theinvention.

FIG. 2 is a circuit diagram of a switch module structure and half-bridgecircuit topology for use with embodiments of the invention.

FIG. 3 illustrates a technique for selectively charging and dischargingthe DC link capacitor in the voltage conversion circuit of FIG. 1 whenoutputting power from the DC power source to the DC bus, according to anembodiment of the invention.

FIG. 4 illustrates a technique for selectively charging and dischargingthe DC link capacitor in the voltage conversion circuit of FIG. 1 whenrecharging a DC power source, according to an embodiment of theinvention.

FIG. 5 illustrates a technique for recharging a DC power source via theDC bus and without use of the voltage conversion circuit, according toan embodiment of the invention.

FIG. 6 is a flowchart illustrating a technique for controlling operationof a voltage conversion circuit in a DC power distribution system whenoutputting power from a DC power source to a DC bus, according to anembodiment of the invention.

FIG. 7 is a flowchart illustrating a technique for controlling operationof a voltage conversion circuit in a DC power distribution system whenrecharging a DC power source, according to an embodiment of theinvention.

DETAILED DESCRIPTION

Embodiments of the invention are directed to a DC power distributionsystem having different or “hybrid” DC power sources connected to acommon DC bus. Each DC power source in the system is connected to avoltage conversion circuit that is configured to condition the DC powerreceived from its respective power source in order to output a voltageto the DC bus having a desired magnitude and direction (i.e.,positive/negative voltage).

Referring to FIG. 1, the general structure of a DC power distributionsystem 10 is shown according to an embodiment of the invention. DC powerdistribution system 10 includes a plurality of power sources thereinthat are connected to a common DC power bus 12. In the embodiment shownin FIG. 1, a pair of DC power sources 14, 16 is shown as being includedin the power distribution system in the form of a photovoltaic (PV)array assembly and a battery. It is recognized, however, that a greaternumber of power sources of various types may be included in the DC powerdistribution system 10, according to embodiments of the invention, withsuch power sources being configured as PV array assemblies, batteries,fuel cells, ultra capacitors, or other known types of DC power sources.

Because terminal characteristics such as voltage, current, power flowdirection, etc., are different for the PV array assembly 14 and thebattery 16 (and for different energy sources in general),conditioning/converting of the power provided from each of the powersources must be performed in order to provide for connection of thepower sources to a common DC bus 12. DC power distribution system 10thus employs voltage conversion or interface circuits 18 to condition aDC voltage output received from a PV array assembly 14 and a DC voltageoutput received from a DC battery 16 to a desired DC bus voltage. Asshown in FIG. 1, a conversion circuit 18 is provided for each powersource 14, 16 and is electrically coupled thereto such that it canreceive power from its respective source and condition the power so asto output a controlled adjustable voltage (i.e., modified voltage) tothe DC bus 12. Beneficially, the structure of the conversion circuits 18included in the system 24 are the same regardless of the type of powersource to which they are connected—as opposed to being “specialized”conversion circuits that are of a specific type based on the type ofpower source to which they are connected, as is typically found inexisting hybrid power systems. As the conversion circuits 18 are of astandardized construction, while still providing flexibility withrespect to the power conversion performed thereby (i.e., output of anadjustable voltage), the construction of the power distribution system10 can be simplified and costs associated therewith reduced.

The general structure of each conversion circuit 18 is shown in FIG. 1,according to an embodiment of the invention. The conversion circuit 18includes a plurality of switches or switch modules 20—forming a switcharrangement/set 22—whose state can be selectively controlled tocondition the DC power output of the PV array assembly 14 and/or battery16 (i.e., the voltage of the output) to a controllable/adjustable DC busvoltage of desired direction and magnitude, identified as V_(adj) inFIG. 1. That is, in operation, the switches 20 in each conversioncircuit 18 function to selectively convert the output voltage providedfrom each of the power sources 14, 16 and regulate the output from theconversion circuits 18 to the DC bus 12, as described in more detailbelow.

An exemplary topology/construction of the switches 20, and anarrangement thereof, is shown in more detail in FIG. 2. Each switchmodule is comprised of an electrical switch 24 and a diode 26.Electrical switches 24 are shown, for illustrative purposes, asinsulated gate bipolar transistors (IGBTs), and diodes are shown asdiscrete ones. However, embodiments of the invention are not limited toIGBTs. Any appropriate electronic switch can be used, such as, forexample, metal oxide semiconductor field effect transistors (MOSFETs)together with their parasitic body diodes, bipolar junction transistors(BJTs), and metal oxide semiconductor controlled thyristors (MCTs). Theswitches and diodes can be made with Silicon (Si), Silicon Carbide(SiC), Gallium Nitride (GaN), or any suitable Wide Bandgap (WBG)material. The switches 20 are arranged in a known half-bridge circuittopology 28 that serves as a fundamental building block for a powerconverter, with the switches 20 being controlled to provide a desiredpower conversion. The half-bridge circuit 28 may be used for one phaseof a single- or multi-phase DC-to-DC converter, with the half-bridgecircuit 28 being controlled to convert an input DC voltage to an outputDC voltage having a desired positive or negative voltage of desiredmagnitude.

Referring back now to FIG. 1, each conversion circuit 18 also includesan inductor 30 coupled to a respective half-bridge circuit 28 (i.e., apair of switches 20) to provide smoothing in the conversion circuit 18.Capacitors 32, 34 are further included in conversion circuit 18—ineither a serial, parallel, or bypass arrangement—to provide circuitstability via charge balancing. That is, capacitors 32, 34 providesubstantial capacitance to buffer energy in case of high frequencymismatch or imbalance of power between the DC power sources 14, 16(e.g., the PV array assembly) and the DC bus 12.

According to one embodiment of the invention, an additional switch 36(i.e., charging switch) is included in the conversion circuit 18 toprovide for a selective connection of the DC bus 12 to the conversioncircuit. Switch 36 may be selectively opened and closed during distinctoperational modes of the conversion circuit 18 where the capacitor 34 isbeing charged or discharged—as will be explained in greater detailbelow. The switch 36 is in an OFF state when the capacitor 34 is beingdischarged and is in an ON state when the capacitor 34 is being charged.By operating the switch 36 in the ON state, the DC bus may be utilizedto provide charging power to the capacitor 34, as will also be explainedin greater detail below. According to embodiments of the invention,switch 36 may be implemented as a MOSFET or IGBT, for example, or anyother appropriate electronic switch previously mentioned herein.

To control actuation/switching of switches 20 and the correspondingamount/level of voltage provided from the DC power sources 14, 16 to theDC bus 12, a controller 38 is provided in each conversion circuit 18that is operationally coupled to the switch arrangement 22. Thecontroller 38 functions to selectively control the state of each switch20 (i.e., the ON-OFF switching/states) in order to control the outputcharacteristic of the conversion circuit 18—with a positive or negativevoltage of desired magnitude being selectively output from theconversion circuit 18. Controller 38 also controls the ON-OFF switchingof charging switch 36.

In operation of conversion circuit 18, the controller 38 receives one ormore inputs regarding operation of its respective DC power source 14, 16and/or operation of the DC bus 12. With respect to the DC bus 12, thecontroller 38 may receive an input regarding the present DC busvoltage—such as from a voltage sensor 40 on DC bus 12—and/or an inputregarding a desired DC bus voltage. With respect to the DC power source14, 16 which the conversion circuit 18 and its respective controller 38is operationally connected to, the controller 38 may receive an inputregarding the output power (voltage and/or current) of the DC powersource 14, 16—such as from voltage/current sensors 42—as well as aninput regarding the type of DC power source to which the conversioncircuit is coupled, such as whether the power source 14, 16 is aunidirectional or bidirectional power source, for example.

Referring now to FIG. 3, and with continued reference to FIG. 1, atechnique 44 is provided—such as would be performed by controller38—that illustrates the operation of the conversion circuit 18 inproviding charge balancing, specifically with regard to the charging anddischarging of capacitor 34 (i.e., the “DC link capacitor”) to bufferenergy in case of high frequency mismatch or imbalance of power betweenthe DC power sources 14, 16 and the DC bus 12. When providing an outputpower from a DC power source 14, 16 to the DC bus 12, the conversioncircuit 18 associated with the power source may be operated in one oftwo modes—a first mode where the capacitor 34 of the respectiveconversion circuit 18 is discharged and a second mode where thecapacitor 34 is charged. As shown in FIG. 3, the operational mode of theconversion circuit 18 is selectively controlled in order to maintain avoltage of the capacitor, V_(C) _(_) _(n), between an upper voltagethreshold, V_(T1), and a lower voltage threshold, V_(T2). Theoperational mode of the conversion circuit 18 is achieved by controller38 via the selection controlling/activation of the switches 20 andswitch 36.

In the first operational mode of conversion circuit 18 where thecapacitor 34 of the conversion circuit 18 is discharged, generallyindicated at 46, both the DC power source 14, 16 and the capacitor 34output power to the DC bus. In providing power from the capacitor 34,the state of switch modules 20 state can be selectively controlled tocondition the power provided therefrom to a desired magnitude. The totalpower output from the DC power source 14, 16 and the capacitor 34 to theDC bus is thus provided as a conditioned power including voltage of adesired magnitude and direction. Operation of the conversion circuit 18in the first mode, with the discharging of the capacitor 34, continuesfor a time, T_(discharge), until the voltage of the capacitor, V_(C)_(_) _(n), decreases to the level of the lower voltage threshold,V_(T2). When the voltage of the capacitor, V_(C) _(_) _(n), reaches thelower voltage threshold, V_(T2), the conversion circuit 18 switches tothe second operational mode.

In the second operational mode of conversion circuit 18 where thecapacitor 34 of the conversion circuit 18 is charged, generallyindicated as 48, the DC power sources 14, and 16 output power only tothe capacitor 34 (with any power flow from the DC source to the DC linktemporarily being stopped) in order to recharge the capacitor 34.Operation of the conversion circuit 18 in the second mode, with thecharging of the capacitor 34, continues for a time, T_(charge), untilthe voltage of the capacitor, V_(C) _(_) _(n), increases to the level ofthe upper voltage threshold, V_(T1). When the voltage of the capacitor,V_(C) _(_) _(n), reaches the upper voltage threshold, V_(T1), theconversion circuit 18 switches back to the first operational mode.

According to an exemplary embodiment, recharging of the capacitor 34 inthe second operational mode may also be performed by the DC bus 12. Thatis, in addition to receiving recharging power from the DC power sources14, and 16, the capacitor also receives recharging power from the DC bus12. In order to enable the supply of recharging power from the DC bus 12to the capacitor 34, the switch 36 in conversion circuit 18 is turned tothe ON state. By supplementing the recharging power provided from the DCpower source 14, 16 with the recharging power from the DC bus 12, therecharging time, T_(charge), of the capacitor 34 can be decreased.

It is recognized that the discharging time, T_(discharge), in the firstoperational mode and the charging time, T_(charge), in the secondoperational mode can vary depending on a number of factors, includingthe voltage level of the respective DC power source 14, 16 and thevoltage level of the DC bus 12. It is further recognized that the uppervoltage threshold, V_(T1), and the lower voltage threshold, V_(T2), willvary/differ (between conversion circuits 18) based on the maximum outputvoltage of the respective DC power source 14, 16 and the voltage levelof the DC bus 12.

Referring now to FIG. 4, and with continued reference to FIG. 1, atechnique 50 is provided—such as would be performed by controller38—that illustrates operation of the conversion circuit 18 for providinga recharging of a DC power source from the DC bus 12 via conversioncircuit 18 when the DC power source is a rechargeable device (e.g., thebattery of DC power source 16), according to an additional embodiment ofthe invention. The technique 50 for charging the DC power source 16includes the selective charging and discharging of capacitor 34 (i.e.,DC link capacitor), and thus in charging the DC power source 16, theconversion circuit 18 associated with the power source may be operatedin one of two modes—a third mode where the capacitor 34 of theconversion circuit 18 is discharged and a fourth mode where thecapacitor 34 is charged. As shown in FIG. 4, the operational mode of theconversion circuit 18 is selectively controlled in order to maintain avoltage of the capacitor, V_(C) _(_) _(n), between an upper voltagethreshold, V_(T3), and a lower voltage threshold, V_(T4). Theoperational mode of the conversion circuit 18 is achieved by controller38 via the selection controlling/activation of the switches 20 andswitch 36.

In the third operational mode of conversion circuit 18 where thecapacitor 34 of the conversion circuit 18 is discharged, generallyindicated at 52, power discharged from the capacitor 34 may beselectively combined with power from the DC bus 12 in order to chargethe DC power source 16. If the voltage of the battery, V_(—Bat), isgreater than the voltage on the DC bus, V_ _(BUS) (i.e., V_ _(Bat) , >V__(BUS) ), then the DC power source 16 is recharged using both power fromthe capacitor 34 and power from the DC bus 12. If the voltage of thebattery, V_ _(Bat) , is less than or equal to the voltage on the DC bus,V_ _(BUS) (i.e., V_ _(BUS) , >=V_ _(Bat) ), then the DC power source 16is recharged using power from only one of the capacitor 34 and powerfrom the DC bus 12. According to one embodiment, power from thecapacitor 34 and power from the DC bus 12 are alternately provided tothe DC power supply 16 to recharge the power supply. According toanother embodiment, only power from the capacitor 34 is provided to theDC power supply 16 to recharge the power supply. In each scenario, poweris provided from the capacitor 34—alone or in combination with powerfrom the DC bus 12—in a controlled fashion via selective operation ofthe of switch modules 20, such that a conditioned power is provided toDC power source 16. The operation of the conversion circuit 18 in thethird mode, with the discharging of the capacitor 34, continues for atime, T_(discharge), until the voltage of the capacitor, V_(C) _(_)_(n), decreases to the level of the lower voltage threshold, V_(T4).When the voltage of the capacitor, V_(C) _(_) _(n), reaches the lowervoltage threshold, V_(T4), the conversion circuit 18 switches to thefourth operational mode.

In the fourth operational mode of conversion circuit 18 where thecapacitor 34 of the conversion circuit 18 is charged, generallyindicated at 54, the DC bus 12 provides power only to the capacitor 34in order to recharge the capacitor 34. In order to enable the supply ofrecharging power from the DC bus 12 to the capacitor 34, the switch 36in conversion circuit 18 is turned to the ON state. Operation of theconversion circuit 18 in the fourth mode, with the charging of thecapacitor 34, continues for a time, T_(charge), until the voltage of thecapacitor, V_(C) _(_) _(n), increases to the level of the upper voltagethreshold, V_(T3). When the voltage of the capacitor, V_(C) _(_) _(n),reaches the upper voltage threshold, V_(T3), the conversion circuit 18switches back to the third operational mode.

According to one embodiment, recharging of the capacitor 34 in thefourth operational mode may also be performed by the DC power source 16.That is, in addition to receiving recharging power from the DC bus, thecapacitor 34 also receives recharging power from the DC power source 16.By supplementing the recharging power provided from the DC bus 12 withthe recharging power from the DC power supply 16, the recharging time,T_(charge), of the capacitor 34 can be decreased.

It is recognized that the discharging time, T_(discharge), in the thirdoperational mode and the charging time, T_(charge), in the fourthoperational mode can vary depending on a number of factors, includingthe voltage level of the rechargeable DC power source 16 and the voltagelevel of the DC bus 12. It is further recognized that the upper voltagethreshold, V_(T3), and the lower voltage threshold, V_(T4), canvary/differ based on the voltage of the DC power source 16 and thevoltage level of the DC bus 12.

Referring now to FIG. 5, and with continued reference to FIG. 1, atechnique 56—such as would be performed by controller 38—for rechargingthe DC power source 16 (e.g., a battery) is illustrated where thevoltage of the battery, V_ _(Bat) , is less than or equal to the voltageon the DC bus, V_ _(BUS) (i.e., V_ _(BUS) , >=V_ _(Bat) ), and onlypower from the DC bus 12 is used to recharge the DC power source 16,according to an embodiment of the invention. In such an embodiment, thearrangement/set of switches 22 in the conversion circuit 18 may bebypassed—such as by turning off switches S_(na) and S_(nc) or switchesS_(nb) and S_(nd) (FIG. 1)—such that the DC bus 12 recharges the DCpower source 16 automatically without the performing of any additionalcontrols.

Accordingly, and as seen in FIG. 5, no charging/discharging of thecapacitor 34 is performed that would vary the voltage thereof betweenupper voltage threshold, V_(T3), and a lower voltage threshold, V_(T4).The recharging of the DC power source 16 is performed until the powersource 16 is fully charged, such that the value of voltage, V_(adj)_(—n) (FIG. 1), is defined as:V _(adj) _(_) _(n)=V _(BUS) −V_ _(Bat)   [Eqn. 1].

Referring now to FIG. 6, and with continued reference to FIG. 1, anoverall technique 60 for operating conversion circuits 18 included inthe DC power distribution system 10 for providing power from hybrid DCpower sources 14, 16 to the DC bus 12 is shown according to anembodiment of the invention. The technique begins at STEP 62 wherein thecontroller 38 of the conversion circuit 18 receives an input regardingthe voltage at which the DC bus 12 is operating. Next, at STEP 64, thecontroller 38 of the conversion circuit 18 receives one or more inputsrelated to the DC power source 14, 16 which the conversion circuit 18and its respective controller 38 is operationally connected to. The oneor more inputs received by the controller 38 at STEP 64 can include aninput such as the output power (voltage and/or current) of the DC powersource 14, 16, as well as an input regarding the type of DC power sourceto which the conversion circuit 18 is coupled, such as whether the powersource is a unidirectional or bidirectional power source, for example.

In a next step of technique 60, the controller 38 of the conversioncircuit 18 receives an input related to the voltage level of the DC linkcapacitor 34 at STEP 66. At STEP 66, the controller 38 also compares thevoltage level of the DC link capacitor 34, V_(C) _(_) _(n), to an uppervoltage threshold, V_(T1), and a lower voltage threshold, V_(T2) betweenwhich the capacitor 34 is to operate. A determination is then made atSTEP 68 as to whether the voltage level of the DC link capacitor 34,V_(C) _(_) _(n), is at the lower voltage threshold, V_(T2). If thevoltage level of the DC link capacitor 34, V_(C) _(_) _(n), is not atthe lower voltage threshold, V_(T2), as indicated at 70, then thetechnique 60 continues at STEP 72 by causing the discharging of the DClink capacitor 34 to provide a voltage output from the conversioncircuit 18, V_(adj). In discharging the DC link capacitor 34, aswitching pattern for the arrangement 22 of switches 20 is determinedbased on the inputs received at STEPS 62 and 64 and the switches areactuated according to the determined switching pattern (such as bytransmitting gate drive signals to the IGBTs of the switches). Indetermining the switching pattern to be implemented, the controller 38determines a direction (positive or negative) and magnitude of a voltageto be output from the conversion circuit 18, V_(adj), that issatisfactory for transmission to the DC bus 12. Once the desired V_(adj)is determined by the controller 38, the controller 38 can determine aswitching pattern for controlling the state of switches 20 that willgenerate this V_(adj) and actuate the switches 20 to cause the DC linkcapacitor 34 to be discharged so as to achieve the voltage V_(adj).Accordingly, both the DC power source 14, 16 and the capacitor 34 outputpower to the DC bus 12.

Conversely, if the voltage level of the DC link capacitor 34, V_(C) _(_)_(n), is at the lower voltage threshold, V_(T2), as indicated at 74,then the technique 60 continues at STEP 76 by charging the DC linkcapacitor 34. In charging the DC link capacitor 34, a switching patternfor the arrangement 22 of switches 20 is again determined based on theinputs received at STEPS 62 and 64 and the switches are actuatedaccording to the determined switching pattern so as to cause thecharging of the DC link capacitor 34 from the respective DC power source14, 16. The controller 38 thereby causes the DC power source 14, 16 tooutput power only to the capacitor 34 in order to recharge the capacitor34. According to one embodiment, the controller 38 also actuates thecharging switch 36 to an ON state to provide recharging power from theDC bus 12 to the DC link capacitor 34. The charging of the capacitor atSTEP 76 continues until the voltage of the capacitor, V_(C) _(_) _(n),increases to the level of the upper voltage threshold, V_(T1), asindicated at STEP 78, with the technique 60 then looping back to STEP 66before continuing.

Referring now to FIG. 7, and with continued reference to FIG. 1, anoverall technique 80 for operating a conversion circuit 18 included inthe DC power distribution system 10 for providing recharging power to arechargeable DC power source—such as the battery of DC power source16—is shown according to an embodiment of the invention. The techniquebegins at STEP 82 wherein the controller 38 of the conversion circuit 18receives an input regarding the voltage at which the DC bus 12 isoperating. Next, at STEP 84, the controller 38 of the conversion circuit18 receives one or more inputs related to the DC power source 14, 16which the conversion circuit 18 and its respective controller 38 isoperationally connected to. The one or more inputs received by thecontroller 38 at STEP 84 can include an input such as the output power(voltage and/or current) of the DC power source 14, 16, as well as aninput regarding the type of DC power source to which the conversioncircuit 18 is coupled, and whether the power source is a unidirectionalor bidirectional power source, for example.

In a next step of technique 80, a determination is made at STEP 86 as towhether a voltage of the DC power source, V_ _(Bat,) is greater than thevoltage on the DC bus, V_ _(BUS) (i.e., V_ _(Bat) , >V_ _(BUS) ). If thevoltage of the DC power source, V_ _(Bat) , is greater than the voltageon the DC bus, V_ _(BUS) , as indicated at 88, then the technique 80continues at STEP 90—where the controller 38 receives an input relatedto the voltage level of the DC link capacitor 34. At STEP 90, thecontroller 38 also compares the voltage level of the DC link capacitor34, V_(C) _(_) _(n), to an upper voltage threshold, V_(T3), and a lowervoltage threshold, V_(T4) between which the capacitor 34 is to operate.A determination is then made at STEP 92 as to whether the voltage levelof the DC link capacitor 34, V_(C) _(_) _(n), is at the lower voltagethreshold, V_(T4).

If the voltage level of the DC link capacitor 34, V_(C) _(_) _(n), isnot at the lower voltage threshold, V_(T2), as indicated at 94, then thetechnique 80 continues at STEP 96 by causing the discharging of the DClink capacitor 34 to provide a voltage output from the conversioncircuit 18, V_(adj). In discharging the DC link capacitor 34, aswitching pattern for the arrangement 22 of switches 20 is determinedbased on the inputs received at STEPS 82 and 84 and the switches areactuated according to the determined switching pattern (such as bytransmitting gate drive signals to the IGBT switches). In determiningthe switching pattern to be implemented, the controller 38 determines adirection (positive or negative) and magnitude of a voltage to be outputfrom the conversion circuit 18, V_(adj). Once the desired V_(adj) isdetermined by the controller 38, the controller 38 can determine aswitching pattern for controlling the state of switches 20 that willgenerate this V_(adj) and actuate the switches 20 to cause the DC linkcapacitor 34 to be discharged so as to achieve the voltage V_(adj).Accordingly, both the DC bus 12 and the DC link capacitor 34 providepower to recharge the DC power source 16.

Conversely, if the voltage level of the DC link capacitor 34, V_(C) _(_)_(n), is at the lower voltage threshold, V_(T4), as indicated at 98,then the technique 80 continues at STEP 100 by charging the DC linkcapacitor 34. In charging the DC link capacitor 34, the controller 38actuates the charging switch 36 to an ON state to provide rechargingpower from the DC bus 12 to the DC link capacitor 34. According to oneembodiment, power is also provided from DC power source 16 to charge theDC link capacitor 34, with a switching pattern for the arrangement 22 ofswitches 20 being determined based on the inputs received at STEPS 82and 84 and the switches being actuated according to the determinedswitching pattern so as to cause the charging of the DC link capacitor34 from the respective DC power source 16. The charging of the capacitorat STEP 100 continues until the voltage of the capacitor, V_(C) _(_)_(n), increases to the level of the upper voltage threshold, V_(T3), asindicated at STEP 102, with the technique 80 then looping back to STEP94 before continuing.

Referring still to FIG. 7, if it is determined at STEP 86 that thevoltage of the DC power source, V_ _(Bat) , is less than or equal to thevoltage on the DC bus, V_ _(BUS) (i.e., V_ _(BUS) , >=V_ _(Bat) ), asindicated at 104, then the technique 80 continues at STEP 106 byrecharging the DC power source 16 using only power from the DC bus 12.In doing so, the arrangement/set of switches 22 in the conversioncircuit 18 may be bypassed—such as by turning off switches S_(na) andS_(nc) or switches S_(nb) and S_(nd) (FIG. 1)—such that the DC bus 12recharges the DC power source 16 automatically without the performing ofany additional controls.

Beneficially, embodiments of the invention provide a standardized andflexible power conversion/interface circuit useable in a powerdistribution system having hybrid DC power sources. The conversioncircuit enables the use of different energy sources and links thoseenergy sources for use in a system by providing a controllable andadjustable voltage output from the conversion circuit based on therequirements of DC bus voltage (or the requirements of the DC powersource, if charging a rechargeable DC power source). By enabling the useof standardized and flexible conversion circuits, a flexible, highlyefficient, bi-directional power flow may be provided in a DC powerdistribution system at a low cost.

A technical contribution of the invention is that it provides acontroller implemented technique for conditioning the DC power receivedfrom respective DC power sources in order to output a voltage to acommon DC bus having a desired magnitude and direction. A controllerassociated with a respective switching circuit controls the switchingcircuit to provide a desired voltage adjustment to a DC voltage of anassociated DC power source, based on a plurality of inputs received bythe controller.

Therefore, according to one embodiment of the invention, a DC powerdistribution system includes a DC bus and a plurality of DC powersources connected to the DC bus each configured to generate an outputpower for transmission to the DC bus, wherein the plurality of DC powersources include at least two different types of DC power sources havingdiffering voltage terminal output characteristics. The DC powerdistribution system also includes a power conversion circuit coupled toeach of the plurality of DC power sources to selectively condition theoutput power generated by its respective DC power source to a DC busvoltage, with each power conversion circuit having a standardizedconstruction so as to be identical to each of the other power conversioncircuits. Each power conversion circuit further comprises a switcharrangement comprising a plurality of switches operable in an open stateand a closed state, a plurality of capacitors arranged to provide acharge balancing in the power conversion circuit, the plurality ofcapacitors including a DC link capacitor, and a controller in operablecommunication with the switch arrangement, the controller beingprogrammed to receive a first input comprising a DC bus voltage presenton the DC bus, receive a second input comprising at least one parameterrelated to operation of the DC power source to which the respectivepower conversion circuit is coupled, determine an adjustable voltage tobe output from the conversion circuit to the DC bus based on thereceived first and second inputs, and selectively control operation ofeach of the plurality of switches in the switch arrangement in order togenerate the determined adjustable voltage.

According to another aspect of the invention, a method of conditioningan output power of hybrid DC power sources in a power distributionsystem includes generating a first output power from a first DC powersource and generating a second output power from a second DC powersource, the second DC power source being a different power source thanthe first DC power source such that the second output power has adifferent voltage characteristic than the first output power. The methodalso includes performing a voltage conversion of the first output powerby way of a first conversion circuit so as to generate a first modifiedvoltage and performing a voltage conversion of the second output powerby way of a second conversion circuit so as to generate a secondmodified voltage, the second conversion circuit having an identicalconstruction as the first conversion circuit. The method furtherincludes providing the first and second modified voltages to a common DCbus to which the first and second DC power sources and first and secondconversion circuits are electrically coupled, wherein performing thevoltage conversion of the first and second output powers by way of thefirst and second conversion circuits each further comprises receiving afirst input comprising a DC bus voltage present on the DC bus, receivinga second input comprising at least one parameter related to operation ofthe DC power source to which the respective power conversion circuit iscoupled, determining a modified voltage to be output from the conversioncircuit to the DC bus based on the received first and second inputs, andcontrolling operation of the respective conversion circuit in order togenerate the determined modified voltage.

According to yet another aspect of the invention, a DC powerdistribution system includes a DC bus and a plurality of DC powersources connected to the DC bus and configured to generate an outputpower for transmission to the DC bus, wherein the plurality of DC powersources include at least two different types of DC power sources havingdiffering voltage terminal output characteristics. The DC powerdistribution system also includes a voltage conversion circuitoperatively coupled to each of the plurality of DC power sources toselectively condition the DC power generated by its respective DC powersource or condition a DC power provided to its respective DC powersource to provide recharging thereto. Each of the voltage conversioncircuits has an identical construction and further includes a switcharrangement comprising a plurality of switches operable in an open stateand a closed state, a plurality of capacitors arranged to provide acharge balancing in the power conversion circuit, the plurality ofcapacitors including a DC link capacitor, and a controller in operablecommunication with the switch arrangement. The controller is programmedto receive a first input comprising a DC bus voltage present on the DCbus, receive a second input comprising at least one parameter related tooperation of the DC power source to which the respective powerconversion circuit is coupled, and determine an adjustable voltage to beoutput from the conversion circuit to the DC bus or to the DC powersource based on the received first and second inputs, the adjustablevoltage comprising a positive or negative voltage of desired magnitude.The controller is further programmed to selectively control operation ofeach of the plurality of switches in the switch arrangement in order togenerate the determined adjustable voltage.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. A DC power distribution system comprising: a DCbus; a plurality of DC power sources connected to the DC bus eachconfigured to generate an output power for transmission to the DC bus,wherein the plurality of DC power sources include at least two differenttypes of DC power sources having differing voltage terminal outputcharacteristics; a power conversion circuit coupled to each of theplurality of DC power sources to selectively condition the output powergenerated by its respective DC power source to a DC bus voltage, witheach power conversion circuit having a standardized construction so asto be identical to each of the other power conversion circuits; whereineach power conversion circuit comprises: a switch arrangement comprisinga plurality of switches operable in an open state and a closed state; aplurality of capacitors arranged to provide a charge balancing in thepower conversion circuit, the plurality of capacitors including a DClink capacitor; a charging switch operable to selectively electricallycouple and decouple the power conversion circuit to the DC bus; and acontroller in operable communication with the switch arrangement, thecontroller being programmed to: receive a first input comprising a DCbus voltage present on the DC bus; receive a second input comprising atleast one parameter related to operation of the DC power source to whichthe respective power conversion circuit is coupled; determine anadjustable voltage to be output from the conversion circuit to the DCbus based on the received first and second inputs; and selectivelycontrol operation of each of the plurality of switches in the switcharrangement in order to generate the determined adjustable voltage. 2.The DC power distribution system of claim 1 wherein, in generating thedetermined adjustable voltage, the controller is further programmed tocause the DC link capacitor to be selectively charged during a capacitorcharging mode and discharged during a capacitor discharging mode.
 3. TheDC power distribution system of claim 2 wherein the controller isfurther programmed to: receive an input on a voltage of the DC linkcapacitor; compare the voltage of the DC link capacitor to an uppervoltage threshold value and a lower threshold voltage value; and causethe DC link capacitor to be selectively charged and discharged based onthe comparison of the voltage of the DC link capacitor to the uppervoltage threshold value and the lower threshold voltage value.
 4. The DCpower distribution system of claim 3 wherein the controller is furtherprogrammed to set the upper voltage threshold value and the lowerthreshold voltage value based on the DC bus voltage and on a maximumvoltage of the respective DC power source.
 5. The DC power distributionsystem of claim 3 wherein the DC link capacitor is charged by therespective DC power source during the capacitor charging mode.
 6. The DCpower distribution system of claim 5 wherein the controller is furtherprogrammed to switch the charging switch to an ON state when in thecapacitor charging mode, such that the DC link capacitor is recharged bythe DC bus and the respective DC power source.
 7. The DC powerdistribution system of claim 1 wherein one of the plurality of DC powersources comprises a battery, and wherein the power conversion circuitcoupled to the battery selectively conditions a recharging powerprovided to recharge the battery.
 8. The DC power distribution system ofclaim 7 wherein the controller is further programmed to cause the DClink capacitor to be selectively charged and discharged duringrecharging of the battery.
 9. The DC power distribution system of claim8 wherein, in selectively charging and discharging the DC linkcapacitor, the controller is further programmed to: receive an input ona voltage of the DC link capacitor; compare the voltage of the DC linkcapacitor to an upper voltage threshold value and a lower thresholdvoltage value; and cause the DC link capacitor to be selectively chargedand discharged based on the comparison of the voltage of the DC linkcapacitor to the upper voltage threshold value and the lower thresholdvoltage value.
 10. The DC power distribution system of claim 1 whereinthe switch arrangement comprises a pair of half-bridge circuits.
 11. TheDC power distribution system of claim 10 wherein each of the powerconversion circuits further comprises an inductor connected to arespective half-bridge circuit, the inductors providing smoothing in thepower conversion circuit, and wherein the inductor may connect to eitherof the half-bridge circuits to further simplify the half-bridge circuit.12. The DC power distribution system of claim 1 wherein the second inputreceived by the controller comprises at least one of an output voltageand current of the DC power source to which the respective powerconversion circuit is coupled and a type of DC power source to which therespective power conversion circuit is coupled.
 13. A method ofconditioning an output power of hybrid DC power sources in a powerdistribution system, the method comprising: generating a first outputpower from a first DC power source; generating a second output powerfrom a second DC power source, the second DC power source being adifferent power source than the first DC power source such that thesecond output power has a different voltage characteristic than thefirst output power; performing a voltage conversion of the first outputpower by way of a first conversion circuit so as to generate a firstmodified voltage; performing a voltage conversion of the second outputpower by way of a second conversion circuit so as to generate a secondmodified voltage, the second conversion circuit having an identicalconstruction as the first conversion circuit; providing the first andsecond modified voltages to a common DC bus to which the first andsecond DC power sources and first and second conversion circuits areelectrically coupled; wherein performing the voltage conversion of thefirst and second output powers by way of the first and second conversioncircuits each further comprises: receiving a first input comprising a DCbus voltage present on the DC bus; receiving a second input comprisingat least one parameter related to operation of the DC power source towhich the respective power conversion circuit is coupled; determining amodified voltage to be output from the conversion circuit to the DC busbased on the received first and second inputs; and controlling operationof the respective conversion circuit in order to generate the determinedmodified voltage; and selectively coupling and decoupling the first andsecond conversion circuits to the DC bus via switching of a chargingswitch in each of the first and second conversion circuits.
 14. Themethod of claim 13 wherein the second input comprises at least one of anoutput voltage and current of the respective first or second DC powersource to which the respective first or second conversion circuit iscoupled and a type of the respective first or second DC power source towhich the respective the first or second power conversion circuit iscoupled.
 15. The method of claim 13 wherein controlling operation of arespective conversion circuit comprises controlling a switch arrangementin the conversion circuit to selectively charge and discharge a DC linkcapacitor in the conversion circuit.
 16. The method of claim 15 whereinselectively charging and discharging the DC link capacitor comprises:determining a voltage of the DC link capacitor; comparing the voltage ofthe DC link capacitor to an upper voltage threshold value and a lowerthreshold voltage value; and causing the DC link capacitor to beselectively charged and discharged based on the comparison of thevoltage of the DC link capacitor to the upper voltage threshold valueand the lower threshold voltage value.
 17. The method of claim 15wherein, in charging the DC link capacitor, the charging switch isclosed such that charging power is provided from the DC bus to the DClink capacitor.
 18. A DC power distribution system comprising: a DC bus;a plurality of DC power sources connected to the DC bus and configuredto generate an output power for transmission to the DC bus, wherein theplurality of DC power sources include at least two different types of DCpower sources having differing voltage terminal output characteristics;a voltage conversion circuit operatively coupled to each of theplurality of DC power sources to selectively condition the DC powergenerated by its respective DC power source and condition a DC powerprovided to its respective DC power source to provide rechargingthereto, wherein each of the voltage conversion circuits has anidentical construction and comprises: a switch arrangement comprising aplurality of switches operable in an open state and a closed state; aplurality of capacitors arranged to provide a charge balancing in thepower conversion circuit, the plurality of capacitors including a DClink capacitor; and a controller in operable communication with theswitch arrangement, the controller being programmed to: receive a firstinput comprising a DC bus voltage present on the DC bus; receive asecond input comprising at least one parameter related to operation ofthe DC power source to which the respective power conversion circuit iscoupled; determine an adjustable voltage to be output from theconversion circuit to the DC bus or to the DC power source based on thereceived first and second inputs, the adjustable voltage comprising apositive or negative voltage of desired magnitude; and selectivelycontrol operation of each of the plurality of switches in the switcharrangement in order to generate the determined adjustable voltage. 19.The DC power distribution system of claim 18 wherein, when the voltageconversion circuit selectively conditions the DC power generated by itsrespective DC power source, the controller is programmed to cause the DClink capacitor to be selectively charged during a capacitor chargingmode and discharged during a capacitor discharging mode; and wherein, incausing the DC link capacitor to be selectively charged and discharged,the controller is further programmed to: receive an input on a voltageof the DC link capacitor; compare the voltage of the DC link capacitorto an upper voltage threshold value and a lower threshold voltage value;and cause the DC link capacitor to be selectively charged and dischargedbased on the comparison of the voltage of the DC link capacitor to theupper voltage threshold value and the lower threshold voltage value. 20.The DC power distribution system of claim 18 wherein, when the voltageconversion circuit conditions DC power provided to its respective DCpower source to provide recharging thereto, the controller is programmedto cause the DC link capacitor to be selectively charged and dischargedduring recharging of the DC power source; wherein, in causing the DClink capacitor to be selectively discharged, the controller is furtherprogrammed to: provide recharging power to the DC power source from eachof the DC link capacitor and the DC bus; or provide recharging power tothe DC power source from only one of the DC link capacitor or the DC busat a given time; and wherein, in causing the DC link capacitor to beselectively charged, the controller is further programmed to providecharging power to the DC link capacitor from at least the DC bus.